Currently, when affixing a torque converter impeller assembly to a cover assembly before positioning it within a vehicle transmission, welding is used to form a seam affixing the two pieces together. The types of welding methods currently used are gas metal arc welding, which is the most common method, laser beam welding and electron beam welding. All three types are fusion welding methods. However, these methods of welding have drawbacks when used in this type of application.
With the aforementioned welding methods, significant joint preparation and design is required since these methods are sensitive to oil and grease being on the surfaces being welded and the joints do not form a simple butt joint. This complicates the operation and maintenance required in the welding process for high volume production, which increases the time require to complete a weld, thus reducing productivity. The cost of filler material also adds to the cost of operation. The desire, then, exists for a low maintenance, high reliability method to join the two assemblies together with minimal operating time per weld. To accomplish this objective, it is also desired to have easy set-up before each weld and good repeatability from one weld to the next, while keeping costs low.
Further, with the three weld methods described above, there are consumables, such as burning gas, which can be environmental concerns. Thus, the desire exists to minimize the associated environmental concerns associated with the welding of the two assemblies.
The torque converter is require to have a continuous leak proof closure, i.e., a hermetic closure, around the seam. This is because the torque converter will contain a fluid under pressure essential to the operation of the torque converter. To accomplish this, it is preferred that there be no gap and filler material between the two assemblies after welding, since this will improve the first time leak proof capability and will help to improve the dimensional integrity by removing distortion from other processes that require more heat along with the use of the fillers. Additionally, by removing the need for filler material and reducing the heat generated at the weld, it will be easier to satisfy all dimensional, joint strength and rigidity requirements, while still keeping the cost of welding to a minimum.
A different type of joining method, that does not require gaps or filler material, is friction welding. Currently, friction welding is used for other types of applications but not for producing torque converter seams. Friction welding does not require fillers and is a type of welding that is easy to set up and repeatable since it is not sensitive to grease and oil on the workpiece surfaces. Friction welding does not have the potential environmental concerns of welding methods that release gas during the welding process. It is also a solid state process that produces strong joints with good dimensional tolerances while assuring a good hermetic seal along the weld seam since the weld is created by diffusion rather than fusion.